Animal allergens are major components of farm, home and animal laboratory dust.

Allergen Exposure

Geographical distributionThe name Swine is applied mainly to domestic animals, though several wild varieties, native to Eurasia and North Africa and introduced to North America and other regions, belong to the same species. (But 16 species of Pigs and Hogs in 8 genera make up the modern family Suidae.) Swine are valuable for their flesh, prepared as Ham, Bacon, and Pork, and for their fat (lard); they also provide many other products, e.g., leather for gloves, footballs, and other articles, and bristles for brushes.

EnvironmentA great majority of US Swine production has moved from open pens to enclosed, mechanized facilities. The trend is toward huge, factory-like farms where Swine are born and bred inside structures that feed, water, and dispose of wastes while controlling ambient temperature. The giant modern farms produce enormous amounts of waste; this has become of increasing concern as a potential source of water pollution.

AllergensNo allergens from this animal have yet been characterised.

Potential Cross-Reactivity

Inhibition experiments have demonstrated that the spectrum of IgE reactivity to Cat serum albumin completely contains IgE reactivity to Swine serum albumin, suggesting that sensitisation to Cat is the primary event. The frequency of sensitisation to Cat serum albumin lies between 14% and 23%. Sensitisation to Swine albumin was found to be between 3% and 10%. About 1/3 of these individuals may experience allergic symptoms following Pork consumption, the Cat-Pork syndrom. Sensitisation to Cat serum albumin should be considered a useful marker of possible cross-sensitisation not only to Swine serum albumin but also to other mammalian serum albumins (1).

Reports in the literature have not differentiated which of the three is predominantly responsible for adverse symptoms, and as with other mammalian allergens, the assumption is reasonable that all three contribute.

Reports in the literature of the atopic sensitisation risk that Swine pose to farmers and other individuals, and of the prevalence of allergic conditions, are contradictory.

An early study reported that Pig farming was a risk factor for asthma, chronic bronchitis, and wheezing during work (5).

Subsequent studies have concurred that Pig farmers have increased wheezing and significantly lower FEV1 measurements than controls, but that few Pig farmers demonstrate atopy as determined by skin-specific IgE tests, suggesting that occupational exposure in Swine confinement buildings is associated only with mild increases of nonspecific, nonatopic airways responsiveness in Pig farmers (6-7).

Further studies, including cross-sectional surveys among Pig farmers, report an increased prevalence of cough, morning phlegm and chronic bronchitis, but not of asthma, despite many factors promoting the manifestation of asthma. Importantly, compared with controls, Pig farmers reported fewer allergies to common allergens and fewer symptoms of atopy in childhood (8, 9). Health-based selection of non-asthmatics for Pig farming, a selection that tends to mask a work-related hazard for asthma, was offered as an explanation for these results (9).

The results of a questionnaire sent to 6,156 randomly selected animal farmers in Denmark, Germany, Switzerland, and Spain showed that Pig farmers were at highest risk for the development of work-related symptoms. A significant dose-response relationship between symptoms and daily hours worked inside animal houses was established for Pig. Self-reported nasal allergies and nasal irritation during work were said to be associated with the development of chronic phlegm (10). A Swiss study concurred that Pig farming was a risk factor for reporting nasal irritation at work (11).

A study conducted among farmers in eastern Poland examined 68 farmers from 17 randomly selected family farms. None of the farmers complained of any symptoms when working with Cows or Pigs. In 13 farmers either positive skin-specific IgE and/or the presence of serum-specific IgE to Cow dander and/or Pig epithelia was found. Seven farmers were positive on skin-specific IgE tests: 2 to Cow epithelium, 2 to Pig epithelium, and 3 to both allergens (12).

In New Zealand, in a postal questionnaire sent to a random sample of 2,500 farmers throughout the country, 77% of the 2,203 who were eligible replied. Asthma prevalence was higher for Horse breeders/groomers (16.5%), Pig farmers (18.2%), poultry farmers (17.4%), and those working with Oats (17.4%) (13).

Furthermore, farmers have more complaints of work-related symptoms of smell impairment, and more often have nasal polyps and hyperaemia of the nasal mucosa. They also have higher levels of myeloperoxidase in nasal lavage (especially dairy farmers and Pig farmers), and a tendency to more-swollen nasal mucosa and lower olfactory threshold (especially grain farmers) (14).

Although reports of atopic sensitisation to Swine do not necessarily concur, some authors conclude that detection of Cow and Swine antigen-specific IgE may be a useful screening tool, although an exact assessment of sensitivity and specificity of the method in a larger population of exposed farmers will be required (15).

Swine farmers may develop Swine Breeder's Lung, a form of extrinsic allergic alveolitis, although this condition does not appear to be commonly reported as associated with Swine farming. A study reported on 2 Pig breeders who had typical symptoms after working in a pigsty. The diagnosis of Swine Breeder's Lung was confirmed by the finding of precipitating antibodies against Pig epidermal components and Pig serum in the patients' sera (4, 16). An earlier study reported that sensitisation against Swine antigens correlated with exposure but not with the presence of symptoms and that a large antigen panel should be used in testing for sensitisation because of the many immunogenic dusts that are present in the air in Swine barns (17). This early study has been supported by a more recent report that demonstrated an increased prevalence of bronchitis, but showed that Swine building workers had no precipitins to antigens found in their environment and no clinical evidence of extrinsic allergic alveolitis. The number of years on the farm, dual exposure with Dairy Cattle, positive skin prick tests, type of piggery, and type of feeding did not change the respiratory health impact of Swine buildings (18).

In healthy subjects, acute inhalation of Swine dust has been shown to cause an influx of inflammatory cells into the airways and increased bronchial responsiveness. The exposure may also cause fever and generalised symptoms. Proinflammatory cytokines appear to be involved in the response to inhaled Swine dust. A significant correlation between the IL-6 response in BAL fluid and exposure to airborne dust endotoxin activity and 3-OH fatty acids was demonstrated (19).

Other reactionsSome Swine diseases are transmissible to humans. Among them are brucellosis, trichinosis, and cysticercosis.